1. Field of the Invention
The present invention relates to improvements in an X-ray image detecting device for detecting X-ray penetration images using solid-state image pickup devices in a panoramic X-ray diagnosis apparatus for medical treatment, particularly for dental treatment.
2. Prior Art
Panoramic X-ray diagnosis apparatuses for medical treatment, particularly for dental treatment are widely used clinically to observe the arrangement of the teeth and the conditions of the dental roots in the mouth of a patient. As an example of such apparatuses, a panoramic photographing apparatus which performs panoramic radiographing by rotating an image detecting device and an X-ray source while maintaining a constant relationship between the image detecting device and the X-ray source, with the head of the patient positioned therebetween, is widely used for dental treatment. A conventional panoramic radiographic apparatus opto-chemically formed images of penetrated X-ray on X-ray sensitive films. This method took a long time for development and was not suited for immediate observation and diagnosis during treatment.
To solve this problem, an art is used for a dental radiographing apparatus to reproduce X-ray penetration images on a monitor unit by receiving slit-passed X-ray on a fluorescent plate to first obtain a visible light image, by forming the image on the image pickup surface of a pickup tube or a CCD image pickup device via an optical lens system and by converting the image to an electric signal. In addition, another art which directly and optically combines a fluorescent surface and an image pickup surface by using optical fiber and transmits images, instead of forming images by using an optical lens system, has been developed.
A prior art related to the above-mentioned technology has been disclosed, in the case of radiographing only one tooth and its surrounding area by using an apparatus (I) which receives X-ray beams from an X-ray source outside the mouth and picks up the beams as a still image by using an arrangement wherein a sensor comprising optical fiber which optically combines an X-ray fluorescent plate and the image pickup surface of an electronic chip, such as a CCD image pickup device, is disposed behind the tooth to be photographed in the mouth (Japanese Laid-open Patent Application No. 60-234645).
Another panoramic radiographing apparatus (II) discloses an art which combines the fluorescent surface image extending in the longitudinal direction of the above-mentioned slit on a small image pickup surface by gradually reducing the diameter of each element of the optical fiber (used to connect a narrow belt-shaped fluorescent surface to a CCD image pickup device) in the direction from the fluorescent surface to the image pickup surface of the CCD image pickup device (FIG. 2 in Japanese Laid-open Utility Model Application No. 63-140907). A third apparatus (III) discloses an art wherein the one end of the optical fiber bundle connected to the fluorescent surface extending in the longitudinal direction of the slit is cut at the surface obliquely to the axis of each element of the fiber bundle and the other end of the fiber bundle is cut at the surface orthogonally to the axis and connected to the image pickup surface of the CCD image pickup device, thereby the image on the fluorescent surface in the longitudinal direction of the slit is reduced and formed on the CCD image pickup device (FIG. 3 in Japanese Laid-open Utility Model Application No. 63-140907 cited above). With these apparatuses (II) and (III), the narrow belt-shaped fluorescent surface is connected via a fiber bundle to the image pickup surfaces of a plurality of CCD image pickup devices and the image signals from the CCD image pickup devices are electrically combined to obtain an X-ray panoramic image on the display screen of a monitor unit.
The above-mentioned solid-state image pickup device, such as a CCD image pickup device, wherein the image pickup surface of the solid-state image pickup device, is connected to an optical fiber bundle, X-ray transmits a visible light image to be formed on the fluorescent surface and the image is observed on the display screen on a monitor unit, has an image pickup surface size of about 5 mm square. This value is far smaller than the longitudinal length (about 150 mm) of the fluorescent surface. It is very difficult to increase the size of the image pickup surface. Even if possible, the cost is assumed to be excessive.
When using the prior art applied to the apparatus (I) for a panoramic radiographing apparatus, its image pickup surface is too small, and all ranges including the upper and lower jaw sections cannot be photographed. When using the art applied to the apparatus (II), it is difficult to uniformly taper (gradually reduce the diameter) the end of each element of the fiber. Even if possible, production cost would be excessive.
As a problem common to both the apparatuses (II) and (III), if the reduction ratio between the image on a divided fluorescent surface and the image formed by the fiber bundle on the image pickup surface of the CCD image pickup device is made larger, the resolution of the image signal from the CCD image pickup device is deteriorated.
In the case of all above-mentioned prior arts, since the solid-state image pickup devices are disposed in the penetration range of the slit-passing X-ray, the electric charges by X-ray irradiation inside the devices accumulate, being in danger of causing the solid-state image pickup devices to break.
The rim of the sealing material for the solid-state image pickup device is generally larger than the image pickup surface thereof and protrudes from the surface. If a plurality of image pickup devices are placed side by side, the rim of the sealing material for a solid-state image pickup device makes contact with the adjacent fiber bundles and the rims of the sealing materials for other adjacent solid-state image pickup devices, causing a problem when arranging the solid-state image pickup devices in an X-ray image detecting device.